The invention relates to a device for measuring a pressure difference within a pulsed column, which can in particular be used for determining the density or level of the interface in pulsed columns of irradiated nuclear fuel reprocessing installations.
In irradiated nuclear fuel reprocessing installations, pulsed columns are frequently used in which an aqueous phase is contacted with an organic phase for bringing about the extraction of uranium, plutonium and/or fission products. To ensure a satisfactory operation of such pulsed columns, it is necessary to accurately check the development of certain parameters, in particular the level of the interface in the decanter, the density of the liquid phases circulating in the column and the weight of a liquid column.
Bearing in mind the radioactivity of the phases processed in the column, it is necessary to use for carrying out such checks and inspections very reliable automatic devices, which in particular satisfy the following requirements:
they must not incorporate parts liable to become defective when in contact with radioactive solutions, PA0 they must satisfy nuclear safety conditions, PA0 they must be insensitive to ionizing radiation, PA0 they must be insensitive to high internal pressure variations due to the pulsation, PA0 they must have an excellent corrosion resistance in the presence of the radioactive solutions processed in the column.
It is known that parameters such as the interface level, the weight of a liquid column and the density of a liquid can be determined on the basis of pressure values at one or more points within the column. Conventionally, the pressure is measured in a pulsed liquid by placing a suitable transducer in contact with the liquid and by converting the pressure into a usable electric signal. A faithful measurement, which is e.g. easy to use is obtained if the transducer has an adequate dynamic response. When the solutions circulated in the column are dangerous or corrosive solutions, it is possible to place a buffer liquid between the diaphragm in contact with the liquid and the diaphragm of the transducer. However, such measuring devices cannot be used in the case of the pulsed columns employed for processing radioactive solutions, due to the considerable difficulties encountered in maintaining them and carrying out repairs.
Furthermore, in such columns, the pressure within the liquid is measured by determining the bubble pressure of a gas such as air. Devices usable for this measurement simply comprise dipping tubes, which issue into the liquid of the column at the points where it is desired to measure the pressure, means for producing a compressed gas into these tubes and means for measuring the pressure within the dipping tubes.
In the case of devices of this type, the only part which is in contact with the radioactive liquid is constituted by the dipping tube, which satisfies the requisite conditions. Thus, the dipping tube undergoes little change over a period of time, can easily be unblocked by injecting an appropriate liquid, no constructional problems are encountered in its production for the purpose of satisfying nuclear safety conditions and it is insensitive to ionizing radiation. Moreover, the pressure measuring means can be constituted in this case by a conventional transducer, because the latter is located outside the column in an accessible area and is only in contact with filtered air.
However, such devices are not suitable for measuring pressure in pulsed columns. Thus, in this case, the pressure within the liquid of the column varies significantly with the pulsations, which causes the liquid to rise in the dipping tubes and there is a variation in the level of said liquid as a function of the pulsation. Therefore, the pressure value measured in dipping tubes not correspond to the pressure of the liquid in the column. This problem is more particularly encountered when measuring the interface level in a lower decanter of a pulsed column operating in a continuous organic phase. Thus, for this measurement, it is necessary to be able to detect a low amplitude pressure variation (e.g. approximately 0.3 millibar/1 cm of interface level variation) and this variation is drowned in a background noise of approximately 300 to 600 millibars due to the pulsation, i.e. a background noise which is 1000 to 2000 times higher. Thus, such a device is not suitable for checking the interface level in a pulsed column.
To obviate this disadvantage, consideration has been given to the improvement of such devices by using different systems for reducing the parasitic phenomena due to pulsation. To this end, pneumatic shock absorbers have been used on the dipping tubes. Consideration has also been given to determining the interface level by measuring the pressure difference between two points P.sub.1 and P.sub.2 of the column by bubbling a gas into so-called "rejected pots", or head pots, as they are sometimes called, which are respectively connected to the liquid level of the column at points P.sub.1 and P.sub.2. However, these systems are not satisfactory. Thus, when using pneumatic shock absorbers, the measuring chain must be calibrated as a function of the operating parameters of the column, i.e. the pulsating pressure, the pulsating frequency, the flow rate, etc. Therefore, when these parameters vary, it is necessary to recalibrate the measuring chain, which is very difficult to carry out.
In the case of the "rejected pots," or head pots, as they are sometimes called, system it is difficult to carry out on an industrial level due to the hydraulic complexity and the large overall dimensions of the circuits, risks of the pipes connecting the pots to the column becoming dirty and problems caused by a sudden variation in the interface level.